In various communication systems, on the basis of a request for miniaturization and higher performance of a device, a small and broadband antenna is in demand. Examples of antennas addressing the request for miniaturization are an inverted-F antenna and a patch antenna. Even if the profile of the inverted-F antenna is lowered (miniaturized) by a metal pin which is short-circuited near a feeding point, antenna matching can be obtained. However, a problem occurs such that the frequency band in which matching is obtained is limited by a small loop passing through the feeding point and the metal pin. Consequently, the height of the antenna adapted to a plurality of broadband wireless systems is necessary.
A patch antenna is constructed by disposing a radiative conductor and a conductive bottom board so as to face each other with an insulating material as an inclusion therebetween. The patch antenna can be thinned and miniaturized. However, the patch antenna also has a problem that the operable band is narrow.
On the other hand, as disclosed in JP-A 2007-124696 (KOKAI), an attempt to broaden the operable band by inserting a magnetic material in the patch antenna is also made. However, the combination of the patch antenna and the magnetic material disclosed in the literature does not always sufficiently satisfy miniaturization and a broader band. The resonance frequency is relatively high like 3.5 to 4.5 GHz.
To make the effect of broadening the band by inserting a magnetic material to an antenna displayed, thickness of 10 μm or larger, preferably, 100 μm or larger is necessary. The dielectric property of the magnetic material exerts an influence on the antenna characteristics and has to have high insulating performance. However, at present, there is no insulating magnetic material having high magnetic permeability in a high frequency band of 3.5 to 4.5 GHz and having a thickness of 10 μm or larger, preferably, 100 μm or larger.